Senior U.S. intelligence and Defense officials told Fox News that to up to 30 former Guantanamo Bay detainees may have returned to the battlefield, surmising that they have formed an alliance with Islamic State and other jihadist organizations including Al Qaeda in Syria.

There could be “as many as to 20 to 30” former Gitmo detainees, some of whom were liberated by the Obama administration within the last three years, suspected of linking up with Islamic State (IS, also known as ISIS and ISIL) and other jihadist groups in Syria, the unnamed sources told Fox News.

The news outlet reported that “of the 620 detainees released from Guantanamo Bay, 180 have returned or are suspected to have returned to the battlefield” where U.S. soldiers are waging a war on terror.

“Of those 180, sources say 20 to 30 have either joined ISIS or other militants groups in Syria, or are participating with these groups from outside countries,” the article explained. “Officials say most of those 20 to 30 are operating inside Syria.”

Top Pentagon officials acknowledged that former detainees who are released do return to the battlefield, but not many.

“We know that some of the detainees that have come out of Guantanamohave gone back to the fight, the battlefield. We’re aware of that and wethink that overall the policy of getting to close Guantanamo is clearlyin the interest of the United States, as the president hasarticulated,” Defense Secretary Chuck Hagel told reporters at the Pentagon today.

“Webelieve that the recidivism is a relatively small fraction of thosedetainees which have been placed into conditions where the risk ofrecidivism is mitigated. But even one would not make someone wearing theuniform very content,” Chairman of the Joint Chiefs of Staff Gen. Martin Dempsey added.

The unnamed official’s revelation vindicated trepidation that American forces would once again face jihadists who had already been removed from the battlefield, noted Fox News, adding that U.S. officials were unable to reveal the identities of the former detainees who have returned to the battlefield.

A number of the released detainees have joined forces with “ISIS, on the ground inside Syria,” revealed Fox News. “Others are believed to be supporting Al Qaeda or the affiliated al-Nusra Front in Syria.”

Some are supporting Islamic extremism from outside the combat zone in Syria by monetarily sustaining jihadists’ operations and propaganda campaigns.

The sources told Fox News that “the former detainees who have joined ISIS in Syria have migrated from the European and African countries which agreed to receive them from the United States. Egypt and Tunisia, as well as six European countries, are among them.”

There are 149 individuals still detained at Gitmo, according to the article, with 80 detainees currently qualified to be transferred out.